1. Field of the Invention
The present invention relates generally to a traffic light, and in particular to a light-emitting diode (LED) based traffic light comprising a dual refractive layers in front of the LEDs to form uniform light projection through generation of multiple images of each LED that are close or partially overlap each other.
2. The Prior Arts
As compared to the traditional incandescent lamps, and other light sources, light-emitting diode (LED) has the advantages of low power consumption, high lighting efficiency and long life span. Traditionally, the LED, however, suffers poor brightness in lighting performance. This drawback has been overcome recently with the development of LED technology. Costs of manufacturing such high brightness LED are sufficiently low for regular lighting purposes. Thus, traffic lights, which must have sufficient brightness in order to provide visual indication to drivers and pedestrians in sun shining days, are now using LEDs as the light source, which reduces not only the overall power consumption, but also the maintenance expense.
An additional advantage of the LED based traffic light is that the sun phantom that often occurs in the incandescent lamp based traffic light in sun shining days can be eliminated and as a consequence, traffic accidents can be reduced.
Nevertheless, the currently available LED based traffic light has still deficiencies due to physical limitation in angle of light projection from the LED. Thus, the drivers and pedestrians who are located outside the available range of projection angle of traffic light cannot clearly identify the lighting status of the traffic light. This limitation cannot be overcome by simply increasing the brightness of LEDs.
Traffic lights with a front cover featuring light refraction to project the light from LEDs to a designated direction are currently available in the market. An example illustrating the front cover structure of the conventional traffic light is shown in FIGS. 1 and 2 of the attached drawings. The front cover, which is designated with reference numeral 10, has an inner, light incidence surface 11 that faces the LEDs of the traffic light. The light incidence surface 11 forms a plurality of raised strips functioning as prisms 13, each corresponding in position to an array of the LEDs and having curved face 131, a straight face 132, a convex lens structure 133, and a vertical face 134. The convex lens structure 133 is comprised of convex lenses 1331 that are lined up in a direction parallel to the raised strips and extend in a transverse direction.
Light from each LED is incident onto the associated prism 13 and is refracted by the faces of the prism 13 and leaving the front cover 10 through a light emission surface 12 in a direction that is downward inclined with respect to the horizon. The light is thus projected to the eyes of the drivers and the pedestrians that are usually located below the traffic light.
However, each prism 13 forms an individual projection, which may overlap each other, leading to alternate bright section 21 and dark section 22. As a consequence, the distribution of the projected light is non-uniform. Further, each individual LED can still be visually identified, although light from the LED has been refracted by the front cover to expand the coverage thereof. This further makes the light distribution non-uniform. Thus, visual observation of the traffic light is still poor.
Thus, the present invention is aimed to provide a traffic light having an enhanced light projection for improving visual observation by drivers and pedestrians.